1. Field of the Invention
The present invention relates to an acceleration estimation device that estimates vehicle accelerations, and a vehicle including the same.
2. Description of the Related Art
The traveling speeds of vehicles can be calculated on the basis of the rotational speeds of its wheels. When the vehicle is rapidly accelerated, however, the wheels may be rotated while sliding against a road surface. When the vehicle is rapidly decelerated (braked), the wheels may be caused to slide against the road surface. In such a case, the speed of the vehicle that can be calculated from the rotational speed of the wheels does not coincide with the actual traveling speed of the vehicle.
Therefore, the acceleration of the vehicle is detected using an acceleration sensor, and the detected acceleration is integrated to calculate the speed of the vehicle.
The acceleration sensor outputs the acceleration as a voltage. Generally, offset exists in the acceleration sensor. Here, the offset in the acceleration sensor refers to a value obtained by expressing a difference between a nominal value of the output voltage of the acceleration sensor at an acceleration of 0 m/s2 and a value of the actual output voltage of the acceleration sensor in terms of units of (m/s2) of acceleration.
The offset varies for each acceleration sensor. JP 10-104259 A discloses a vehicle longitudinal acceleration estimating device that removes an unnecessary component of an acceleration sensor for detecting a longitudinal acceleration to calculate an estimated value of the longitudinal acceleration.
In the longitudinal acceleration estimating device disclosed in JP 10-104259 A, the change in an output voltage of the acceleration sensor is frequency-analyzed and is classified into changes due to DC offset, changes due to temperature drift, changes due to road conditions, changes due to acceleration/deceleration of a vehicle, and changes due to pitching of a vehicle body. A Karman filter is used to extract only a variation component having a higher frequency than a particular frequency from a detected value of the longitudinal acceleration by the acceleration sensor.
This causes a variation component due to DC offset and a variation component due to temperature drift respectively having low frequencies to be removed from the detected value of the longitudinal acceleration. As a result, the estimated value of the longitudinal acceleration is not affected by changes with time and changes in temperature.
When the vehicle is rapidly accelerated or decelerated, however, the vehicle body is inclined by pitching. That is, the front of the vehicle body rises at the time of rapid acceleration, and lowers at the time of rapid deceleration. Even when the vehicle is traveling at constant speed, the vehicle body is slightly pitched. This causes a component of a gravitational force to be exerted on the acceleration sensor for detecting the longitudinal acceleration. As a result, the detected value in the acceleration sensor includes an offset and is affected by the component of the gravitational force.
In the longitudinal acceleration estimating device disclosed in JP 10-104259A, an unnecessary component in a particular frequency band can be removed from the detected value in the acceleration sensor. However, the effect of the component of force of gravity due to pitching in a frequency band other than the particular frequency band cannot be removed. Therefore, the longitudinal acceleration of the vehicle cannot be accurately estimated.